Even though the institutional owners most heavily invested in the midstream energy sector largely maintained their total holdings during the second quarter, a gap emerged between buyers and sellers as major midstream players grappled with low prices and lackluster financials, an S&P Global Market Intelligence analysis showed.

The knock-on effects of low commodity prices permeated second-quarter earnings. S&P Capital IQ estimates showed a mixed bag for second-quarter revenues and earnings per share, but most of the largest companies still missed their consensus normalized EPS estimates.

While declining share values resulted in a nearly 8% second-quarter loss for the Alerian MLP Index that tracks major midstream master limited partnerships, institutional investors seemed to favor entities undergoing consolidation.

ONEOK Inc. experienced a 14% uptick in institutional ownership, according to the Form 13F data. Ahead of its June 30 merger with subsidiary ONEOK Partners LP, big asset managers BlackRock Inc., Vanguard Group Inc. and State Street Global Advisors Inc. increased their combined holdings by 15.4 million shares, or 32.5%. MPLX LP, which had the third-largest increase in institutional holdings during the second quarter, is in the process of dropping down assets from Marathon Petroleum Corp. to lower the partnership's capital costs and put it in a better position to proceed with M&A opportunities.

Ownership of institutional shares in Energy Transfer Partners LP skyrocketed 50%, which was tied to the partnership's merger with Sunoco Logistics Partners L.P. completed in April. "Probably the vast majority of that is going to be previous Sunoco institutional shareholders," OppenheimerFunds Inc.'s Brian Watson told S&P Global Market Intelligence. "I did notice a couple of new names, so there was still some institutional buying outside the merger impact."

Williams Cos. Inc., on the other hand, saw activist asset management firm Scopia Capital Management LP sell its 4.8 million-share stake during the second quarter, following in the footsteps of Keith Meister's Corvex Management LP and Stephen Mandel's Lone Pine Capital LLC. Meister backed down in September 2016 after threatening a proxy fight unless Williams put "world class" executives on its board, but he kept selling his Williams holdings.

Williams Partners LP, meanwhile, gained two new institutional investors that bought a combined 6 million shares.